1. FIELD OF THE INVENTION
The present invention relates to an optical disk of the type in which the recording and reproduction of data are effected by using a semiconductor laser, an optical disk recording and reproducing apparatus and a copy preventive method for an optical disk which are capable of protecting the stored data from being copied on another optical disk.
2. DESCRIPTION OF THE RELATED ART
The importance of software has been greatly recognized due to the recent popularization of personal computers, work stations, etc. As a result, various methods have been proposed for the purpose of protecting the software, e.g., commercially available programs and data bases recorded on recording mediums are protected from being copied onto other recording mediums.
The copy preventive methods heretofore proposed in the art include, for example, copy preventive methods of a software key type in which the length of each software recording sector is altered intentionally and other copy preventive methods of a hardware key type such as disclosed in Japanese Unexamined Pat. Nos. 60-145501 and 60-175254 in which defects such as unalterable flaws or holes are formed on a recording medium and their position information or pattern is discriminated.
However, the copy prevented methods of the software key type have generally the disadvantage of easy decoding, and various apparatus capable of cleverly copying copy-protected software have already been available commercially. Thus, the methods of this type have substantially failed to provide effective protection.
Also, the copy preventive methods of the hardware key type are disadvantageous in that a software supplier is required to perform a hardware treatment on a recording medium for every software, that is the formation of a hardware key by a physical treatment, e.g., the formation of flaws or holes or the removal of a part of a recording material, and this results in an increased manufacturing cost. Particularly, in the case of an optical disk, the formation of such a hardware key itself is not easy due to the complicated manufacturing process of the optical disk.